Dehumidification of fluids



reams Apr. 12, 1949 EEHUMIDIFIQATION F FLUIDS William S. W. McCarter,Bala-Cynwyd, Pa., as-

signor to Attapulgus Clay Company, Philad phia, la a corporation ofDelaware No Drawing. Application July 22, 1943,

Serial No. 495,959 I 4 Claims. (01. 210-425) The present inventionrelates to the preparation and use of improved dehumidifying ordehydrating agents, and particularly synthetic silicates of the metalssuch as magnesium, calcium,and aluminum, or mixtures thereof.

Fluids such as gases, vapors, or liquids may be freed of moisture bycontacting them with substances which absorb water, but which remaininert to the fluid. Many materials have been suggested as dehumidifyingagents, but the indus trially useful ones are few and expensive. Forexample. adsorbents which have been used commercially as dehumidifyingagents include silica gel, activated alumina, and activated carbon.

Other mineral adsorbents, i. e., natural clays comprising mixedsilicates, have been proposed as desiccants. Clays such as fullers earthand bentonite, even when activated under the most favorable conditionshave been found to be markedly inferior to the agents of the presentinvention for dehumidifyin purposes. In many industrial operations itisessential that very dry gas be used, and to produce such a dry gas itisnecessary that the drying agent remove all, or substantially all, ofthe moisture from thegas. The drying of ordinary adsorbent clays toremove free moisture produces materials which will remove gmss amountsof moisture from gases passed through such materials, but enough watermay remain in the eflluent gases to render them unfit for certain uses-Thermal treatment of the clays at temperatures up to about 220 F.results in the removal of all free moisture and improves the dryingcharacteristics of the clays, but fails to produce dehumidifying agentscapable of removing substantially all moisture from a gas. The moistureadsorptive properties of the clays may be further improved by heating attemperatures substantially above 220 F., for

example, 250 F. to 700 F. under such conditions as to remove all of thefree moisture and a portion of the combined water, but, even claysactivated in this manner are less eillcient as dehumidifying agents thanthe synthetic silicates of the present invention.

I have found that superior dehumidifying agents comprising syntheticsilicates of metals may be prepared by reacting in aqueoussolutionanalkalimetalsilicateandasaltofametal capable of forming awater-insoluble silicate.

While I prefer to utilizethesilicates of magnesium, calcium, orahuninum,adsorptive silicates of other metals such as barium, beryllium, andzirconium may also be "employed. ,The insoluble silicate produced by theabove-reaction is thoroughly washed with water .to remove soluble salts,and is thereafter dried and activated byoheating at temperatures between220 F. and 60 F.

In accordance with my invention, an alkali metal silicate is dispersedin sufficient water to dissolve the compound, and this solution is addedto a second solution containing a water-soluble salt' of a metal capableof forming a waterinsoluble silicate. While chemically equivalentamounts of alkali metal silicate and watersoluble metal salt may beemployed, I prefer to have present in the reaction mixture, an excess ofmetal salt over that required for complete reaction with the alkalimetal silicate. The mixture is then heated, preferably at its boilingpoint, for a period of time sufllcient to complete the reaction, wherebythere is produced a waterinsoluble product comprising the metalsilicate. silicates having a ratio of metal oxide to $102 within therange of 1:1 to 1:4 may be produced. The insoluble silicate is thenseparated from the reaction mixture by suitable means, for example, bydecantation, filtering, or centrifuging, and the product may then bewashed free of soluble salts, dried to a suitable volatile mattercontent, and reduced to particles of desired size.

In carrying out my process, I may employ commercially available alkalimetal silicates having a ratio of Na'zOzSiOa or K20:Si0a of 1:1 to 1:4.The silicates may be used in aqueous solution of desired concentration,and theratio of Na:O:SiO: or K20:S10z may be adjusted by the addition ofsuitable quantities of NaOH or KOH. Commercial sodium silicate, such asN" brandsilicate having a ratio of Na:O:SiOz of 1:322, and a Baumgravity of 41, has been found satisfactory for use. Alkali metalsilicates produced by the treatment of silica or other highly siliciousminerals with alkali metal hydroxides, oxides,-

peroxides, or'carbonates, may also be used. For

- example, materials containing alkali metal silicates produced byfusing fullers earth, bentonite, or other naturally. occurringsilicates, with an alkali metal carbonate, or by treating such 3naturally occurring silicates with an alkali metal hydroxide solution atelevated temperatures, may be satisfactorily employed. Insofar as thewatersoluble metal salts are concerned, I prefer to use the chloride orthe sulfate, although other soluble salts may be employed. Whilesatisfactory results may be obtained using chemically equivalent amountsof a soluble metal salt, based upon the alkali content of the alkalimetal silicate employed, it is not necessary to do so in all cases, asthe completion of the reaction may be favored by having present anexcess of the metal salt. The concentrations of the solutions employedmay vary over a wide range, for example, from 1% up to saturation at theboiling point of the solution or mixture of solutions. The temperatureat which the reaction is carried out is preferably that which isnecessary to maintain the solution or mixture of reactants at itsboiling point, however, higher or lower temperatures may be utilized. Ingeneral, temperatures of from 150 F. to 400 F. are suitable,

sufficient pressure being maintained upon the reaction mixture toprevent substaintial loss of water therefrom. The reaction time willvary considerably, depending upon the quantities and concentrations ofthe reactants, the degree of agitation of the reaction mixture and thetemperature at which the reaction is carried out. In some cases theformation of the metal silicate may be completed in a few hours, whereasin other cases the reaction may require 10 to 15 hours or more. Themetal silicate, upon completion of the reaction, may be freed of solublesalts by washing with water, and then dried to a suitable volatilematter content (water content) prior to reduction of the silicate todesired particle size. The drying and thermal activation of the silicateis accomplished by heating at a temperature from 220 F. to 600 F., andpreferably from 275 F. to 400 F. Depending upon the method of applyingthe metal silicate in the dehumidification of fluids, the particle sizewill vary. The particle size of the silicate may be of the order of 4-8mesh or 10-20 mesh when the fluid to be'dehydrated is to be passedthrough a bed of the silicate. A finer mesh size may be utilized whenthe fluid to be dehydrated is intimately mixed with the silicate, andthe silicate thereafter removed by filtration or other. means. Thevolatile matter content of the silicate may range from 5% to 12% byweight, and is preferably of the order of 7% to 11%.

The various brands of sodium silicate which are exemplary of those whichmay be used in accordance with this invention are given in the followingtable.

Brand ffgf i NazO SiO: mo 3: 11;

Percent Percent Percent Degrees Na metasrlicate- 1:1 29. 1 28. 2 42. 7solid 1:2 18. 36. 46. 0 69. 3 123.22 8. 9 28. 7 62.4 41.0

"S" brand 1:3.9 6. 3 24. 6 69. l 33.

adsorption tower.

parts by weight of water and this solution was added to the solutionfirst mentioned with vigorous stirring. The quantity of MgClafiHaOemployed was slightly in excess of that required for complete reactionwith the sodium silicate. The mixture was refluxed for 2 hours at itsboiling point and the resulting water-insoluble magnesium silicate wasthen filtered from the reaction mixture, and washed free of solublesalts with water. The filter cake was broken up, air-dried and screenedto 10-30 mesh.

The granular magnesium silicate was then activated by heating at varioustemperatures to obtain samples having different volatile mattercontents, and the samples were tested to determine their dehumidifyingcharacteristics. The dry air capacity (D. A. C.) was determined bypassing a measured volume of air of known and constant humidity throughthe known weight of sample contained in an adsorption tower at constanttemperature humidity at F). The effluent air from the adsorption towerwas passed through a moisture-detection tube containing magnesiumperchlorate, and the adsorption tower and contents, as well as thedetection tube, were weighed periodically to determine the amount ofmoisture adsorbed and the time at which moisture was first detectable inthe emuent air from the The dry air capacity of the samples representsthe per cent water adsorbed, based on the original weight of the samplebefore any water appears in the eflluent air. The equilibrium capacity(E. C.) represents the per cent water adsorbed when the moisture contentof the air introduced into and withdrawn from the adsorption tower isthe same. The per cent volatile matter (V. M.) is the total volatilematter driven oil. by heating the sample at 1800 F. to constant weight.The results obtained are shown in the 2. The process of Example 1 wasrepeated, with the exception that 212 parts by weight of MgCl:.6HO wasreacted with 390 parts by weight of 0 brand sodium silicate, the sodiumsilicate being slightly in excess of that required to react with theM8C12.6H2O. The dehumidification efficiency of the resulting product isshown in the following table.

Activating Dehumidif g Adsorbent Conditions E eiency Heating 'iemp.,Time Pei-Cent D A E 0 F. Hour V. M. I

3. The process of Example 1 was repeated using various brands of sodiumsilicate with MgC1:.6H:O, the latter being slightly in excess of thequantity required for complete reaction with the sodium silicate. Theresulting granular products were activated by heating at 350 1''. for 3hours, and then tested for their dehumidiflcaticn efficiencies. with thefollowing results:

4. 130 parts by weight of 09.61: was dissolved in 3000 parts by weightof water and the resulting solution was introduced into a reactionvessel provided with a stirrer. A second solution was made up consistingof 344 parts by weight of "6 brand sodium silicate and 1500 parts byweight of water, andthis solution was added to the solution firstmentioned with vigorous stirring. The mixture was refluxed for 2 hoursat its boiling point, and the water-insoluble calcium silicate resultingfrom the reaction was flltered from the mixture and washed with water toremove soluble salts. The fllter cake was broken up, air-dried andscreened to 10-30 mesh. The resulting granular calcium silicate was thenactivated by heating and the product then tested for dehumidifyingefflciency, with the following results:

Activating Oon- Delmmidil Adsorbent ditions E dency Bea Per- 2?" ra acent D. A. c. 15.0.

' Hours V. M.

5. The process of Example 4 was repeated using 133 parts by weight ofAlz(S04)a. The dehumidifying efliciency of the granular aluminumsilicate thus produced was determined and the results are shown in thefollowing table:

Activating Con- Dehumidil gAdsol-bent ditions ltiiil ri ency HeatingPer- 2 .Timo, cent D. A. o. no.

' Hours V. M.

While herein 1 have described my invention with particular reference tothe production of synthetic silicates by the reaction in aqueoussolution of an alkali metal silicate with the salt of a metal capable offorming a water-insoluble metal silicate, such silicates may besatisfactorily subjected to activation by treatment with ammonium saltin aqueous solution, prior to thermal treatment. The formation ofwater-insoluble metal silicates by the reaction of an alkali metalsilicate with a water-soluble metal salt in the presence of an ammoniumsalt such as ammonium chloride, sulfate, or nitrate, has also been foundto yield adsorbents of improved dehumidifying eiflciency.

Theactivated metal silicateadsorbents prepared in accordance with myinvention may be employed to partially or completely dehumidify avariety of fluids including gases such as air, oxygen, hydrogen,nitrogen, and hydrocarbon gases such as methane, ethane, propane,butane, isobutane, and the corresponding olefln gases or mixturescomprising any two or more of such gases. A variety of other compoundsmay likewise be dehumidifled or dehydrated including hydrocarbon oils ordistillates, benzene, toluene, xylene, halogenated hydrocarbons.alcohols, esters, ethers, ketones, and the like.

At such time as the dehumidifying efliciency of the metal silicateadsorbent decreases through moisture adsorption to an extent such thatthe eiliuent gas contains more than a tolerable amount of moisture, theadsorbent properties thereof may be regenerated by heating attemperatures of the order of 220 F. to 600 F., and preferably at 220 F.to 400 F. Such regeneration may be carried out at ordinary or reducedpressure, and in the presence or absence of air or other gas introducedfrom an extraneous source.

I claim:

1. The method of dehumidifying-fluids, which comprises intimatelycontacting a fluid containing moisture with a water-insoluble metalsilicate at a temperature conducive to the adsorption of said moistureby said silicate, said silicate being prepared by reacting in aqueoussolution an alkali metal silicate and a water-soluble salt of a metalcapable of forming a water-insoluble silicate, separating the insolublesilicate from said solution, washing said silicate to remove solublesalts, and heating the washed silicate at a temperature between 220 F.and 600 E.

E2. The method of dehumidifying fluids. which comprises intimatelcontacting a fluid contain- 0 ing moisture with magnesium silicate at atemperature conducive to the adsorption of said moisture by saidsilicate, said silicate being pre-' pared by reacting in aqueoussolution sodium silicate and a water-soluble salt of magnesium,

05 separating the magnesium silicate from said soluproduced by othermethods of snythesis. For example, a basic carbonate of a metal, such asmagnesium basic carbonate, may be treated with silica, water, and alkaliat an elevated temperation. washing said silicate to remove solublesalts, and heating the washed silicate at a temperature between 275 F.and 400 F.

3. The method of dehumidifying fluids, which comprises intimatelycontacting a fluid containing moisture with calcium silicate prepared byreacting in aqueous solution sodium silicate and a water-soluble salt ofcalcium, separating the calcium silicate from said solution, washingsaid silicate to remove soluble salts, and heating the washed silicateat a temperature between 275 F. and 400 F.

4. The method of dehumidifying fluids, which comprises intimatelycontacting a fluid containing moisture with aluminum silicate preparedby reacting in aqueous solution sodium silicate and a water-soluble saltof aluminum, separating th aluminum silicatefrom said solution, washingsaid silicate to remove soluble salts, and heating 7 8 the washedsilicate at a' temperature between Number Name Daze 275F. and 400 1''.1,745,952 Prutzman Feb. 4, 1930 WILLIAM s. w. MOCARTER. 1,932,153Btowener Nov. 17, 1931 1,939,860 Montgomery Dec. 19, 1933 REFERENCES cum5 1,959,348 cummins May 22,1934 The following references are of recordin the 2990-741 zubnn 1937 m i this 2,101,315 Rembert Feb. 1, 1933 e 92,133,527 Caldwell June 20, 1939 UNIT D STATES PATENTS 2,359,343 wmdmOct. 3, 1944 me -.S'.-- NOV. 6, 24'2,171 o q'peim'et a! May 31, 1991OTHER REFERENCES 321: gf 1:22 Merck; Index, published in 1930 by Merck &1"193039 Krause IIIIII Sept: 1211913 which may Wham] mm 28, 1928 1 foundin Div. 49. Page 312, lines 6 to 17, second 1,686,353 -Hall Oct. 9, 1929

